Materials may be classified as:

FERROMAGNETICFERROMAGNETICstrongly attractedstrongly attracted to magnets to magnets

iron, steel, cobalt, nickel

PARAMAGNETICPARAMAGNETICslightly attractedslightly attracted by strong magnets by strong magnetswood, aluminum, platinum, oxygen

DIAMAGNETICDIAMAGNETICslightly repelledslightly repelled by strong magnets by strong magnetszinc, bismuth, sodium chloride, gold

Magnetism is a property of charge in motion.Magnetism is a property of charge in motion.

Orbiting electrons (negative charges in motion) Orbiting electrons (negative charges in motion) in the atom produce a magnetic field.in the atom produce a magnetic field.

The domain theory is used to explain whyThe domain theory is used to explain whysome materials are, or may become, magnetic.some materials are, or may become, magnetic.

No one knows exactly whyNo one knows exactly whymoving charges cause magnetism.moving charges cause magnetism.

BASIC LAW OF MAGNETISMBASIC LAW OF MAGNETISM

Like poles repel; unlike poles attract.Like poles repel; unlike poles attract.

Although it is possible to isolate positiveAlthough it is possible to isolate positiveand negative charges, it is impossible to and negative charges, it is impossible to isolate isolate NORTHNORTH and and SOUTHSOUTH magnetic poles. magnetic poles.

Magnetic monopoles do not exist.Magnetic monopoles do not exist.

Even though magnetic properties areEven though magnetic properties aresimilar to electric properties, it issimilar to electric properties, it is

erroneous to directly relate positiveerroneous to directly relate positiveand negative electric charges toand negative electric charges tonorth and south magnetic poles.north and south magnetic poles.

The north magnetic poleThe north magnetic poleis is notnot caused by protons, caused by protons,nor is the south magneticnor is the south magnetic

pole caused by electrons!!!!pole caused by electrons!!!!

The force between magnetic poles follows a lawThe force between magnetic poles follows a lawsimilar to the similar to the Law of Universal GravitationLaw of Universal Gravitation

and and Coulomb’s Law for ElectrostaticsCoulomb’s Law for Electrostatics..

Universal GravitationUniversal Gravitation F = G (m1m2)/d2

ElectrostaticsElectrostatics F = k (q1q2)/d2

MagnetismMagnetism F = k (M1M2)/d2

Magnetic fields surround magnets.Magnetic fields surround magnets.

Field lines point from North to SouthField lines point from North to Southoutside the magnet.outside the magnet.

N S

Click here to view some magnetic fields.

TheThe number of field linesnumber of field linesis known asis known as Magnetic FluxMagnetic Flux..

The unit of magnetic flux is theThe unit of magnetic flux is the WEBERWEBER,,named in honor ofnamed in honor of Wilhelm Weber..

The The amount of flux linesamount of flux linesper unit area per unit area is known asis known asMagnetic Flux DensityMagnetic Flux Density..Magnetic Flux Density is Magnetic Flux Density is measured in measured in TESLASTESLAS,,named in honor ofnamed in honor ofNikola Tesla..One Tesla is one Weber per square meter = 1 Weber/mOne Tesla is one Weber per square meter = 1 Weber/m22..

Magnetism became associatedMagnetism became associatedwith currents when with currents when Hans Christian Oersted

noticed a compass movenoticed a compass movenear a wire with a currentnear a wire with a current

in the very early 19th century.in the very early 19th century.

A magnetic field surrounds a current-bearing wire.A magnetic field surrounds a current-bearing wire.

The direction of the magnetic field can be determinedThe direction of the magnetic field can be determinedby the “Right Hand Rule for a Current-Bearing Wire.”by the “Right Hand Rule for a Current-Bearing Wire.”

““Grasp wire with right hand so that thumbGrasp wire with right hand so that thumbpoints in the direction of conventionalpoints in the direction of conventional

(positive) current. Your fingers circle the(positive) current. Your fingers circle thewire in the direction of the magnetic field.”wire in the direction of the magnetic field.”

Click on the following links to view computerClick on the following links to view computersimulated examples of how electricity andsimulated examples of how electricity andmagnetism are necessarily “linked” together.magnetism are necessarily “linked” together.

• magnetic field around a current-bearing wire: magnetic field around a current-bearing wire: Link, , link• Lenz’s Law: Lenz’s Law: Link• Faraday’s Magnetic Field Induction Experiment1:Faraday’s Magnetic Field Induction Experiment1: Link• Faraday’s Magnetic Field Induction Experiment2: Faraday’s Magnetic Field Induction Experiment2: Link• AC Generator: AC Generator: Link• DC Generator: LinkDC Generator: Link• Lorentz Force: LinkLorentz Force: Link• magnet moving in and out of coil (movie): Linkmagnet moving in and out of coil (movie): Link

Applications of Electromagnetic RelationshipsApplications of Electromagnetic Relationships

ElectromagnetsElectromagnets Electric MotorsElectric Motors

GeneratorsGenerators